1. Field of the Invention
The invention is directed to systems and methods for determining the heading angle of a vehicle.
2. Description of the Known Art
The global positioning system (“GPS”) is a space-based global navigation satellite system. Generally, the system provides reliable positioning and timing services to worldwide users on a continuous basis anywhere on or near the Earth which has an unobstructed view of four or more GPS satellites.
GPS systems using two antennas can be utilized to determine the heading (e.g., yaw), roll and pitch of a vehicle. Attitude refers to the heading, roll and pitch of a vehicle. For attitude determination, some constraints can be applied, such as the distances between the two GPS antennas, or highly bounded attitude information such as the ranges of expected pitch and roll angles for land navigation, machine control, and guidance. Additionally, it is known to introduce a distance constraint to a Kalman filter procedure. However, this distance constraint requires the linearization to be accurate. Because the distances between the two GPS antennas are generally very short, typically at or around 1 meter, the design matrix, which is used to process the GPS measurement data to provide intermediate calculations toward a final position or attitude estimate, cannot be determined precisely from the float solution. Thus, the Kalman filter process could diverge if the non-linearity is not taken into consideration correctly. Another issue is that the real-time kinematic float solution may not satisfy the baseline length constraints well after the integer ambiguity resolution procedure is applied.